The objective of this study is to elucidate the intracellular interactions of the HIV regulatory protein Nef with host cell activities. Early in the HIV-1 infective process this retrovirus expresses regulatory proteins, with the Nef transcript representing nearly 80% of total viral mRNA. In vivo infectivity by SIV and HIV is achieved in the absence of Nef expression, but there is an absolute requirement for Nef in the development of the immunodeficiency. This essential activity of the Nef protein in the development of AIDS has not been defined. We have established that the Nef protein associates with a member of the p21-activated kinase (PAK) family, which is known to initiate activation pathways in those cells which can be infected by the HIV virus. In the periphery, these cells include T cells and macrophages, and in the CNS, brain macrophages and to a lesser degree astrocytes. We have recently found that Nef expression enhances T cell activation. The effect of expression of this pathogenic regulatory protein on macrophage function will be examined. The biochemical mechanism for these Nef-mediated alterations in both T cells and macrophages and the nature of the Nef-PAK association will be defined.